The classification of CMPDs is based on the lineage of the predominant proliferating cells and the prominence of marrow fibrosis, taken together with a constellation of clinical and laboratory features.

The World Health Organization (WHO) classification system6 identifies seven conditions under the category of CMPDs, as shown in Table 45.1.

Tefferi9 classified ET, PV, and IMF as CPMDs. The CMPDs, in turn, are members of a broader class of

Table 45.1 WHO classification of chronic myeloproliferative diseases

Chronic myelogenous leukemia [Ph chromosome, t (9;22) (q34;q11), BCR/ABL positive] Chronic neutrophilic leukemia

Chronic eosinophilic leukemia (and the hypereosinophilic syndrome)

Polycythemia vera

Chronic idiopathic myelofibrosis (with extramedullary hematopoiesis)

Essential thrombocythemia

Chronic myeloproliferative disease, unclassifiable

Adapted from Jaffe et al.6

"clonal" stem cell processes operationally designated as the chronic myeloid disease groups (CMDs).

The classification of chronic myeloid disorders is shown in Table 45.2. The classification system is somewhat arbitrary, as features may overlap between myelodysplastic syndrome (MDS) and CMPD. The identification of specific disease-causing mutations similar to the Ph chromosome in CML is hoped to pave the path toward a molecular classification system of CMDs.

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